The invention relates to a filter element especially for filtering fluids.
It is known that different types of filter material can be used in known filter elements, combined to produce an optimum filter behavior for the particles to be filtered out and the fluid flowing through. For example, it is known from DE 44 43 158 A1 to use a melt-blown material as the filter medium in a gas stream together with a carrier material serving exclusively for stabilization.
It is also known from WO 96/34673 to locate a plurality of filter layers made of a melt-blown material on a carrier layer in a hollow cylindrical filter element. The layers then form together a replaceable filter element that can be placed in a filter system.
The sequential arrangement of nonwoven filter media made of synthetic fibers with staggered filter fineness is known from U.S. Pat. No. 5,496,627 and WO 95/17946, with the filter fineness of the filter layers increasing in the flow direction.
It is also known from U.S. Pat. No. 5,427,597 and WO 96/34673 to arrange several filter layers or only one filter layer of a nonwoven web made by the melt-blowing process on a carrier layer which serves primarily for stabilization. The filtering effect of the carrier layer is negligible in comparison to the other layers.
The processing of synthetic filter nonwoven webs, especially melt-blown nonwoven webs, to produce filters requires the use of support materials. For example, metal wire cloth or even cellulose-based filter papers are used for this purpose. When cellulose-based supporting layers have heretofore been used, only filter layers exhibiting a much smaller degree of separation than the synthetic filter layer have been used. In such case, the supporting layer has no influence on the filtration properties of the overall arrangement but requires a considerable amount of space. Overall, in this known concept, only a certain part (for example, 30%–50%) of the volume of the overall arrangement is used for filtration.